Application of sulfonated biochar-based magnetic catalyst for biodiesel production: Sensitivity analysis and process optimization

•Sulfonated biochar-based magnetic catalyst has been synthesized and applied in the biodiesel production reaction.•RSM-based CCD approach was applied to optimize the process condition.•Maximal biodiesel efficiency was 98.11% at a temperature of 74.8 °C within 4.8 h.•Biodiesel yield declined from 97.52% to 80.64% after the sixth run. The sulfonated magnetic porous biochar-based solid catalysts have a significant potential to replace homogeneous acid catalysts in order to decrease corrosion issues and the environmental risks brought on by homogeneous acid catalysts. For this purpose, produced biochar from the rice husk pyrolysis at 700 °C was employed for the synthesis of a biochar-based magnetic acid catalyst. The base structure of the catalyst was modified and magnetized using different ratios of ZnCl2 and FeCl3. The magnetic porous biochar was sulfonated with two sulfonation agents including H2SO4 and ClSO3H. Characteristic analyzes of BET (Brunauer, Emmett, and Teller), Scanning Electron Microscopy, vibrating-sample magnetometer, Fourier Transform Infrared Spectroscopy, Energy-Dispersive X-ray Spectroscopy, and elemental analysis were used to investigate the physicochemical properties of the synthesized catalysts. The magnetic biochar-sulfonated with ClSO3H was evaluated as the selected catalyst in the biodiesel generation process from oleic acid (OA) as a representative of bio-oils. The central composite design (CCD) based on the response surface methodology (RSM) was used to optimize the process and examine the effectiveness of various parameters, including catalyst concentration based on the OA weight (3–15 wt.%), experiment duration (1–5 h), MeOH: Oil molar ratio (5–25), and reaction temperature (40–100 °C), on the efficiency of biodiesel generation. The optimum yield was achieved at 98.11% under the optimal condition, which included an experiment duration of 4.8 h, catalyst concentration of 9.9 wt.%, MeOH: Oil ratio of 16:1, and reaction temperature of 74.8 °C. [Display omitted]